What is strabismus?

Strabismus or squint is a deviation to the position of the eye so that both eyes are no longer directed towards the same point. The condition usually develops in childhood, but can also occur in adults.

There are various forms of strabismus:

  • The commonest form of strabismus, convergent strabismus, involves one eye (sometimes both) turning towards the nose
  • Divergent strabismus means the eye turns outwards
  • The eye can also turn upwards (sursum vergens) or downwards (deosum vergens)

Squint occurs in about 2-5% of children and is more common after the first year of life. The abnormal eye position is experienced as ugly, which often means these children are teased. However, strabismus is not only an aesthetic problem. The main reason for the detection and treatment of squint at an early age is to prevent the eye from becoming lazy (amblyopia).

Lazy eye

When squint occurs at a young age the child rarely suffers from double vision. The duplicate image is suppressed within the brain. If the image provided by one eye is suppressed for a long time, this eye will not develop properly, causing vision to deteriorate (lazy eye) with certain visual details no longer clear. When both eyes develop squint and images are supressed alternatively, the chance of developing amblyopia is small. A lazy eye will not heal without treatment and can only be successfully treated in children up the age of approximately 7 years.

If squint develops after the eighth year of life or in adulthood, the ability of the brain to suppress the duplicate image is lost. Squint will therefore not lead to lazy eye because the brain functions are already fully developed. The person will therefore suffer from double vision, as signals from both eyes are converted into separate images.

More information on strabismus or lazy eye? Make your appointment at Focus Eye Clinic today.

Strabismus: symptoms

A high degree of strabismus is immediately apparent. However, smaller deviations are barely observable (micro-strabismus) and appear less serious. This is certainly not the case, as the consequences will be the same; even in cases of micro-strabismus, a lazy eye with poor visual acuity is often the result.

In strabismus which develops after the first 8 years of life the chance of developing a lazy eye is small, but double vision can occur. A sufferer might squeeze one eye shut, hold his or her hand in front of one eye or complain of double vision. Furthermore, people with squint can present with motor symptoms such as stumbling and grabbing for but missing an object placed next to them, as well as find it difficult to estimate distances.

What are the causes of strabismus?

People see with both eyes. The images from both eyes are combined by the brain into a single image. This ability for dual vision develops in the first 6-7 years of life. If this development is disrupted, strabismus may be the result. The causes of squint in children are not always clear, but hereditary and environmental factors probably play a role:

  • Hereditary predisposition
  • Ophthalmic abnormalities
  • Refractive disorders (e.g. high degree hypermetropia), unequal eye strengths
  • Medical problems experienced during birth and shortly afterwards
  • Cranial nerve disorders, the most common cause of late onset strabismus. A malfunctioning cranial nerve might be the result of other pathology such as heart attack and diabetes, etcetera.
  • Premature birth, smoking or drug use during pregnancy

How is strabismus or squinting treated?

Strabismus treatment can be long-term and consists of:

  • Glasses, with or without prisms
  • Exercises
  • Lazy eye treatment
  • Strabismus surgery

Lazy eye treatment

If strabismus is accompanied by a lazy eye, the lazy eye must be treated before any eye muscle correction is carried out. This treatment includes the following methods: covering the good eye, prescription glasses and in certain cases, eye drops.
Strabismus surgery will only be proposed at a later stage if this seems necessary.

Strabismus surgery

For some children the eye position will eventually need to be corrected. Strabismus surgery or eye muscle surgery will then be performed in which the eye muscles attached to the outside of the eyeball are made either weaker or stronger by moving or shortening them. This can be done on one or both eyes.
In about 80% of cases a single surgical procedure is sufficient; however, on occasion a second surgical procedure will be necessary in cases of under or over correction, for example. Before carrying out ophthalmic procedures in older children and adults it is very important to fully investigate the risk of post-operative double vision beforehand. Sometimes the brain is so well adapted to an existing abnormal eye position that it becomes impossible to correct squint for cosmetic purposes without causing double vision. In such cases, surgery is not a viable solution.

More information on strabismus or lazy eye? Make your appointment at Focus Eye Clinic today.